The present invention relates to an electronic apparatus, and more particularly to an electronic apparatus which is adapted to drive a load circuit based on an electric power supplied from a power feed unit having a supply power with voltage varying in time, for example, an electronic apparatus that operates a load circuit with an electric power supplied from a generator such as a thermoelectric converting element.
FIG. 7 is a schematic block diagram of a conventional electronic apparatus. In FIG. 7, an electronic apparatus 700 is provided with a power feed unit 10 having a supply power with voltage varying in time, a load circuit 30 operating on a power supplied by the power feed unit 10, and a voltage detecting circuit for detecting a voltage of a power supplied by the power feed unit 10 and outputting a voltage detection signal based on the voltage to the load circuit.
In such an electronic apparatus, a reduction in size and weight also requires one to reduce the size and weight of the power feed unit 10, resulting in a tendency toward decrease in power in the power feed unit 10. This in turn induces a tendency decrease the power supply voltage to be supplied by the power feed unit 10.
Under such a circumstance, a conventional electronic apparatus has incorporated a generator and etc., which was configured as shown in FIG. 7 by a power feed unit 10 to have electric power or voltage varying in time, a voltage detecting circuit 20 for detecting an output voltage of the power supply unit 10 to determine a power feeding ability of the power feed unit 10 based on the detected voltage and outputting a voltage detection signal dependent upon the power feeding ability of the power supply unit 10, and a load circuit 30 operating on a power supplied by the power feed unit 10 and controlled in operation by the voltage detection signal.
In the above configuration, because the voltage detecting circuit 20 is limited to its detectable minimum voltage value (minimum detection voltage), when the power voltage supplied by the power feed unit 10 decreases below the minimum detection voltage value, the voltage detecting circuit 20 cannot detect a voltage of the power feed unit 10. In the meanwhile, the power and voltage supplied by the power feed unit 10 tends to decrease, as stated above. Moreover, the output voltage of the power feed unit 10 is detected while the load circuit 30 is consuming the power supplied by the power feed unit. Consequently, the output voltage of the power feed unit 10 is affected by a power consuming state in the load circuit 30, besides the reduction in the output voltage of the power feed unit 10.
That is, in the conventional electronic apparatus as described above, there is often a case that the voltage detecting circuit 20 cannot detect an output voltage of the power feed unit 10. The voltage detecting circuit 20 cannot grasp a power feedability of the power feed unit 10, and hence cannot output a voltage detection signal dependent upon the power feedability. That is, there was a problem in that it was impossible to control the operation of the load circuit 30 depending upon the power feedability of the power feed unit 10. Furthermore, even if the voltage detecting circuit 20 can detect an output voltage of the power feed unit 10, the output voltage of the power feed unit 10 is determined by a power consuming state in the load circuit 30. Due to this, the power feedability of the power feed unit 10 cannot be grasped by the power voltage supplied by the power feed unit 10. As a result, the voltage detecting circuit 20 might output a voltage detection signal irrespective of the power feedability of the power feed unit 10. Thus there was a problem in that the operation of the load circuit 30 was controlled in a manner irrespective of the power feedability of the power feed unit 10.
Particularly, if the conventional electronic apparatus configuration is adopted for a watch that operates on an electric power generated by a thermoelectric converting element due to a temperature difference between the arm and the ambient air, the thermoelectric converting element as the power feed unit 10 requires an increased number of series P-type and N-type columns to increase a time period during which is generated a power voltage higher than a minimum detection voltage for the voltage detecting circuit 20. It is accordingly difficult to accommodate the thermoelectric converting element within the watch. In order to accommodate the thermoelectric element within the watch, there is no way but to decrease the number of the series columns. This, however, increases the time period during which the voltage detecting circuit 20 can not detect the voltage of the thermoelectric converting element. In the case that the number of the series columns has to be decreased, there is a possibility that no detection can be made. On the other hand, if the thermoelectric converting element can be accommodated within the watch with the number of series columns left large, the thermoelectric converting element is increased in internal resistance. This may cause the voltage of the thermoelectric converting element to drop the moment the power of the thermoelectric converting element is supplied to the load circuit 30, resulting in an increase in the time period for which the minimum detection voltage of the voltage detecting circuit 20 is not reached. Meanwhile, where the load circuit 30 consumes much power, there may be a case that the voltage of the thermoelectric converting element does not exceed the minimum detection voltage. This increases the time period during which the voltage detecting circuit 20 can not detect the voltage of the thermoelectric converting element. In a worst case, there is a possibility that no time period is obtained for detection. Even if the voltage detecting circuit 20 can detect a voltage of the thermoelectric converting element, it is difficult to grasp from such a voltage a power feedability of the thermoelectric converting element. As stated above, where the conventional electronic apparatus configuration is adopted for a watch, the power generating ability of the thermoelectric converting element is difficult to be grasped, resulting in difficulty in controlling the operation responsive to the power generating ability.
For example, where the conventional electronic apparatus configuration is adopted for the watch so that a generated power by the thermoelectric converting element as the power feed unit 10 is converted into a voltage-increased power by a boosting circuit as the load circuit 30 and supplied to an accumulator and watch drive circuit also as the load circuit 30, the power generating ability of the thermoelectric converting element is difficult to be grasped because of the above-described reasons with a result that it is difficult the boosting circuit to set a voltage magnification in compliance with a power generating ability or the like. Thus there has been encountered a problem of difficulty in generating a voltage-increased power suited for charge storage on the accumulator or for the watch drive circuit, and hence a problem of difficulty in utilizing a power generated by the thermoelectric converting element.